Permanent magnet motor



Aug v3 1943- J. M. NAUL i PERMANENT MAGNET MOTOR Filed April 13, 1942 2 Sheets-Sheet l J. M. NAUL 2,325,915

PERMANENT MAGNET MOTOR Aag. s, 1943.

Filed April 13, 1942 2 shets-sheet 2 3 PWR/Wto@ gan/ned Patented Aug. 3, 1943 PERMANENT MAGNET MOTOR James-M. Naul, Fanwood, N. J., assignor to The Singer N. J., a

Manufacturing Company, Elizabeth, corporation of New Jersey Application April 13, 1942, Serial No. 438,674

13 Claims. (Cl. 172-36) This invention relates to direct-current motors, particularly of the separately-excited type in which small permanent magnets are used to supply the eld Iiux.

More particularly, the invention is concerned with lightweight motors of very small size especially adapted for service which requires frequent reversals of rotation and for locations where space and weight are important factors.

As an indication of the size of motor with which I am concerned, a motor built according to the invention has outside housing dimensions of approximately one inch in width, one inch in height, and one and seven-eighths inches in length, and a rotor diameter of aboutone half of one inch. In motors of this size the space and weight requirement of the terminals alone may be considerable relative to the entire motor. This relation is aggravated in the case of conventional direct-current motors in which four terminals must be provided so that the armature winding may be externally connected reversely relative to the field winding to reverse the direction of rotation of said motor. f

It is an object of this invention, therefore, to provide a small, compact, lightweight directcurrent motor having only two external connection terminals and being readily reversible in rotation by reversing the polarity of the applied voltage.

A further object of this invention is to provide a small, reversible direct-current motor having a. small permanent magnet for supplying the field flux, including provision for the ready replacement of said magnet without removal of the rotor or disturbance of the bearing alignment or initial air gap concentricity.

With the above and other objects in view as will hereinafter appear, the invention comprises the combination and arrangement of parts hereinafter set forth and illustrated in the accompanying drawings of a preferred embodiment of the invention and the advantages attained thereby will be ready understood by those skilled in the art;

In the accompanying drawings:

Fig. l is an enlarged longitudinal sectional view taken through an improved motor embodying the invention.

Fig, 2 is a bottom plan View of the motor shown in Fig. 1.

Fig. 3 is a vertical section taken substantially on line 3-3, Fig. 1.

Fig. 4 is a perspective view of the improved motor.

Fig. 5 is a disassembled perspective view of the motor.

Referring more specifically to Fig. 1, there is shown an electric motor comprising a U-shaped frame I of non-magnetic material such as aluminum preferably formed by a die-casting process and having a block-like body portion 2 and spaced-apart parallel limb portions 3 and 4 adjoining said body portion. A block-like end-cover 5 of non-magnetic material is secured to the free ends of limb portions 3 and 4 by means of screws 6 and forms with said frame member I a partially closed housing within which is positioned a rotatable armature member R. The limbportions 3 and 4 are formed with inner face portions I which conform to the peripheral shape of the armature R as may be seen best in Fig. 3. The end-cover 5 is formed with peripheral shoulder portions 8 which provide locating surfaces against which the face portions I may be seated. Within the body portion 2 is located a bearingreceiving recess 9 which communicates with the exterior through a radial oil duct I0. Similarly, within the end-cover 5 is located a bearingreceiving recess II and a radial communicating oil duct I2.

The rotatable armature R is of conventional construction and comprises a laminated magnetic core I3 to which is applied a winding I4 connected to the commutator I5. The core I3 and commutator I5 are secured to a shaft I6 by a. press fit onto a straight-knurled portion thereof. Insulation end-pieces II and collars I3 are employed to insulate the winding I4 from metallic parts of the rotor. Anti-friction bearings I8 pressedonto each end portion of shaft I6 are seated within recesses 9 and II and are provided 'with thin, flexible disc seals 20 to prevent o-il leakage through the bearings to the interior of the housing. Felt washers 2| and 22, are positioned adjacent the ball-bearings I9 within the respective recesses 9 and II to provide oil reservoirs which maintain a supply of lubricating oil for the bearings. The end-cover 5 is provided with an aperture .'ia through which extends an end portion of the shaft I6.

Thus far, I have described a partially closed non-magnetic housing with a. rotatable armature journaled within said housing. It is to be noted that all additionalparts needed to complete an operative motor are secured to the outside of the housing and do not require for their assembly any displacement or disarrangement; of the parts thus far described.

The limb portion 4 is radially thicker than the limb portion 3 and is provided with tapped holes 23, 24 adapted to receive motor-mounting screws (not shown). A transverse slot 25, as seen in Fig. 5, is provided in the limb 4 for receiving a y brush assembly later to be described herein.

The body portion 2 is formed with two finished plane parallel surfaces 26, 21 (Fig. 5), which serve as accurate locating surfaces to provide proper spacingand alignment for po1e-pieces28. v Ear portions 29 are extended laterally from the limb portions 3 and 4 to provide guiding and locating surfaces to facilitate the proper positioning of plate-like pole-pieces 28. These pole-pieces, as seen best in Fig. 5, are formed from low-reluctance magnetic material and present at rectangular -body portions 30 at one end and pole-face portions 3l at the other end which are transversely curved to conform to the periphery of the armature core I3. The two pole-pieces 28 are secured in intimate face-to-face contact with the surfaces 26 and 2l respectively, by means of headed screws 32 which extend through the pole-l pieces andare threaded into the body portion 2 of lthe frame I.

completely embrace the coreportion I3 of the l armature R and to form therewith an air gap of sufliciently low reluctance. 'It is of course contemplated that the pole pieces 28 may be secured Furthermore, the pole-pieces are notched to provide shoulder portions 33 which eect the pole-face portions because of the extensive supporting area provided by the plane parallel surfaces 26 and 2l of the frame I. Further, the draw bolt 35 may be omitted entirely and the magnet held between pole-pieces 28 by a tight push t.

It is seen that the U-shaped eld magnet built up from the permanent magnet 34 and the polepieces 28 embraces the body portion 2 of the frame l and is positioned with the long dimensions of the pole-pieces parallel to the axis of the rotatable armature. This arrangement provides a simple and compact structure in which the pole pieces cooperatel with the frame to form a partial closure for the armature. It is clear that by positively securing the pole-pieces against the extenin the frame I in other suitable ways as, for example, by direct insertion within the die-cast metal during the casting of the frame itself, in whch case fastening screws 32 are'unnecessary The closing link in the magnetic eld circuit is provided by a small block-shaped permanent magnet 34 preferably made from an aluminum, nickel, cobalt, iron alloy, known generally in the trade as Alnico, and employed herein to furnish the eld flux for the motor. This material is particularly well suited for this application due to its high magnetizing force as well as its ability to retain its magnetism, even under adverse conditions. The .permanent magnet 34 is formed so that the two opposite faces 34B and 34b present opposite magnetic polar-ities." These faces are ground plane and parallei and are positioned to form with surfaces 26 and 2'! respectively opplanar surfaces of considerable extent which receive in intimate ace-to-face contact the' body portions 3d ci the pole-pieces 28'as seen best in Figs. 2 andv 4.. A non-magnetic draw bolt 35 extends through one pole-piece body, lies within an external groove 3E.formed in the permanent magnet 34, and is threaded into the opposite polepiece body. By drawing up this bolt 35 the permanent magnet is clamped securely between the pole-pieces to form tight joints having a minimum magnetic reluctance. The groove 3G may be readilyprovided for in the magnet casting and requires no further nnishing. The curved poleface portions 3i of the pole-pieces 28, due to their arched form, are highly resistant to deections in a radial direction. which is an important considerationfin maintaining a fixed air gap. The body' portions 3@ are slightly deflected inwardly to grip the magnet when. the draw bolt 3d is tightened but this deflection' does not appreciably sive coplanar surfaces provided jointly by the housing and the magnet, as described, the air gap is held rigid and constant thereby providing a motor which maintains uniform performance over long periods of use. y

The brush-holder assembly comprises a U- positioned within the brush-boxes, are held radially and resiliently against the commutato'r I5 bymeans of helical wire springs 44 which press down on top of the brushes, and which are wound around the shanks of screws 40 and are hooked over the connector lugs 42 as seen best in Fig. 3.

It is important that the magnetic circuit Afor the field flux comprising the permanent magnet and associated pole-pieces have a low magnetic reluctance in order to utilize theV permanentmagnet'material most eiciently. This is effected by making the contacts at the joints between' planar surfaces of pole-piece and magnet of sufcient area and by'supplying suiiicient clamping pressure at said joints. Further, it isy of advantage, to keep the shape of the permanent magnet as simple as possible in order to avoid diiicult y castings and to require only a minimum of finishing. This 'is especially true of high-grade permanent magnet materials such as Alnico which is notoriously diicult to'machine. Accordingly, I have provided a magnetic circuit which uses as a ux source a small block of highgrade permanent magnet material having only two plane parallel faces which need to be finished ground. Y Y

Itis evident from this description that the replacement of the permanent magnet 34 requires but the simplest manipulation. Removal of draw bolt 35 releases the magnet which is then removed without any disturbance to or disarrange'- ment of the armature, the pole-pieces or the bearing alignment. 'A replacement magnet or the same magnet remagnetized is inserted, boli.

35 replaced and tightened, and the motor is ready to run again. Y

The operation of the motor herein disclosed will be apparent from the foregoing description. It is merely necessary to apply a direct-current voltage of proper magnitude to the connector ings ifi tc energize the motor for rotation. Reverse It is to be 2,325,915 3 rotation is easily enected by simply reversing the stantially plane parallel end faces of opposite polarity of the applied voltage. polarity which form with surface portiom of said Prom the foregoing it will have provided magnet motor be perceived that I a compact, lightweight permanent material is removably POSi` said motor to supply the eld provision for ready replacet magnet without disturbbm-mg machine eld' structure non-magnetic material, a

thereof, a permanent form with opposite surface portions of said frame substantially coextensive coplanar surfaces, polepieces positioned in face-1:04am: contact with said coplanar surfaces and removably secured to said frame.

rorniedwimexmnnat by said im a rotor in the frame journaled bearingnapermanentbarmasnethaving dat sides and extending longitudinally beyond said frame end to engage the ends of said magnet in surface-to-surface contact.

6. In a dynamoelectric machine having a nonmagnetic'irame in which is journaled a, rotatable armature; a built-up eld structure comprising a permanent bar magnet positioned externally adjacent oneend of said frame and having subinwhichasmallblockofperma-Y l1- sides, bearings carried frame substantially coextensive coplanar surfaces, pole-pieces positioned in face-to-face oontact with said copianar surfaces and removably secured to said frame, including adjustable clamping means for holding the permanent magnet securely between said pole-pieces.

7. An electric motor comprising a Irame formed with external by said frame, a rotor in the trame journal 8. An electric motor comprising a nonnetic frame fonned with external dat sides, bearto-surface contact, and a nou-magnetic draw bolt connecting the extended ends of said pole-pieces ior clamping the same upon the permanent magnet the frame end portions.

10. A dynamoeleetric machine eld structure comprising a frame of non-magnetic material, a pair of plate-like pole-pieces secured to opposite being removably the exterior of the housing,

12. An electric motor comprising a nommagnetic frame formed with external flat sides, bearings carried by said frame, a magnetic rotor core in the frame journaled in said bearings,

flat sides, bearings carriedy tact, and extending in the opposite direction to form pole-face portions positioned to partially embrace the rotor core.

13. An electric motor comprising a generally rectangular frame, bearings carried by said frame, a magnetic rotor core in the frame journaled in said bearings, a block-shaped permanent magnet positioned externally of the frame with the magnetic axis transverse tothe direction of the rotor axis, pole-pieces detachably secured intermediate their ends to opposite faces of said frame and connected at one end to the ends of the permanent magnet, terminating at the opposite end in pole-face portions which partially encompass the rotor core.

JAMES M. NAUL. 

